Bright zinc plating



Patented Mar. 1, 1938 PATENT OFFICE BRIGHT ZINC PLATING VincentMattacotti, Matawan, N. 1., assignor to Hanson-Van Winkle-MunningCompany, Matawan, N. J., a corporation of New Jersey No Drawing.

Application September 28, 1985,

Serial No. 42,671 I 6 Claims.

This invention relates in general to the electro-deposition of zinc, andmore particularly to the electro-deposition of zinc ina bright orlustrous form from alkali cyanide baths.

An important object of my invention is the obtaining of a firmlycoherent protective electrodeposit of metallic zinc, on iron and otherconductive surfaces, in a bright or lustrous form.

The invention is applicable quite generally to 10 alkali cyanide zincsolutions, but will be described for the purpose of clear illustrationin connection with the use of an aqueous solution made up of zinccyanide, sodium cyanide and caustic soda. In order to confer upon alkalicyanide zinc solutions the property of producing a firmly coherentprotective and bright or lustrous zinc deposit, I employ as an additionagent one or more ketones which are soluble in or miscible with thesolution and not susceptible to unfavorable reaction with any of itscomponents under the conditions of use. Typical examples of ketoneswhich I have found effective for the purpose stated are acetone, methylethyl ketone, diethyl ketone, quinone and furoin. For the purposes ofthe present invention, ethyl aceto acetate is to be understood asincluded within the term ketone, since it appears to act in an analogousor equivalent capacity as a brightening agent for cyanide zinc plating.With respect to the furoin o mentioned, it is noted that this materialis miscible with the bath in the sense that it may be maintainedsuspended by stirring or agitation, and in such operations, as forexample barrel plating, it does not require any objectionable spe- 0191manipulation to maintain it so distributed or suspended throughout thebath that it can perform its function as a brightening agent. While thevarious ketones and allied products have been named as the brighteningagents, I

wish it to be definitely understood that they do not all have theproperty of conferring upon the zinc deposit the luster or brightnesswhen immediately introduced into the solution, but most of them acquirethis property after a relatively short ageing period varying fromseveral hours to several days. The acquirement of this property may behastened by operating the bath electrolytically or by previouslyconditioning the ketone by treatmentwith a condensation catalyst such soas sulphuric acid, hydrochloric acid, caustic soda, caustic potash,lime, sodium cyanide, and the like. The conditioning of anyelectrolytically conductive mixture or solution of the ketone and thecatalyst may be considerably accelerated by pass- 5 ing a currentthrough it. While I am unable to state Just what chemical change occursin the ketone by the conditioning treatment or the ageing in the bath, Iam nevertheless able to definitely state the operations necessary to theat tainment of the desired brightening function, and wish it to beunderstood that the definition of the agents as ketones must accordinglyinclude whatever materials result from such conditioning or ageingtreatment.

To clearly illustrate the preparation of the 10 bath, I shall refer toone specific example thereof which will give satisfactory results. Suchbath may be made up of a water solution containing the followingingredients:--

, Methyl ethyl ketone (not conditioned) "an--- 25 Two to three times theabove quantity of brightener, say 30 cc. per liter of the conditioned 25ketone or 75 cc. per liter of the non-conditioned ketone, may beemployed without unfavorable effect upon the deposit, and less than theamount stated, say about as low as one-half such amount, may be employedwith correspondingly varying degree of brightening action, but theamount stated represents what appears to be an optimum quantityconsidering the factors of practical eifect and economy.

In the conditioning of the ketone prior to its 35 introduction into thebath, it may be treated, for example, with 2 to 5% concentratedsulphuric acid and allowed to stand for 24 hours, or electrolyzed for 2or 3 hours, and thereafter the mixture added directly to the bathwithout separa- 40 tion or neutralization, as I find this quantity ofacid may be safely added to an alkaline bath of the type specified. Ifdesired, however, thesulphuric acid may be neutralized with an excess ofcaustic soda, before introducing the brightener into the plating bath.In the case of ageing the ketone in the bath instead of previouslyconditioning it by a catalyst, the quantity is preferably greater, asspecified in the above formula. Such a quantity will developsatisfactory brightening qualities on standing idle for several days orby operating the bath for several hours.

-IThe bath may be used for the deposition of zinc at temperaturesvarying, for example, from water.

room temperature to 130 F., and at current densities varying, forexample, from 10 to 50 amperes per square foot. These limits oftemperature and current densities are not actual limits, but merelyrepresent operating conditions which are well within the range oisatisfactory performance. Soluble anodes are preferable but notessential. The soluble anodes may be straight zinc, zinc aluminum, zincmercury, or zinc aluminum mercury, but the performance of thebrightening function does not depend upon the selection of theparticular type of anode employed.

Slight traces of nickel cyanide or cobalt cyanide or nickel sulphate orcobalt sulphate, or a mixture of any of these, may be employed with theketone addition agent. Such nickel and cobalt salts may be employed, forexample, in about the proportions of A; oz. per gallon, and in somecases enhancethe brightness obtaining with the ketone.

The plated articles, upon removal from the bath, may with advantage besubjected to a bright dip composed of, for example, .5% nitric acid andIn employing this clip, the articles, upon removal from the bath, arefirst rinsed, then dipped in the bright dip for a few seconds, thenagain rinsed, and finally dried.

In general, it is noted that the brighteners herein referred to appearto work better if the free cyanide content of the bath is not too high.So far as observed, the anode or cathode efiiciency is not substantiallyafl'ected by the presence of the brightener or addition agent, and thepermissible current density is higher than in ordinary cyanide zincplating. Furthermore, the deposition of the zinc may be continued forprolonged periods far beyond those necessary to the attainment of aprotective thickness of deposit, without sacrificing the quality orappearance. In fact, it has One or more of the addition agents described.may be employed in the bath, the total quantity thereof correspondingin general with the amount of the addition agent already recited.Furthermore, admixtures of other addition agents for brightening orimproving the color of the deposit may be employed with one or more ofthe ketones.

I claim:

1. An alkali cyanide zinc plating bath comprising as an addition agentone or more ketones selected from the group consisting of acetone,methyl ethyl ketone, diethyl ketone, quinone, furoin, and ethyl acetoacetate.

2. An alkali cyanide zinc plating bath comprising as an addition agentfrom 5 to '75 cc. per liter of methyl ethyl ketone.

3. An alkali cyanide zinc plating bath comprising as an addition agentfrom 5 to 75 cc. per liter ketone selected from the group consisting ofacetone, methyl ethyl ketone, diethyl ketone, quinone, furoin, and ethylaceto acetate.

4. An alkali cyanide zinc plating bath comprising as an addition agentfrom 5 to 30 cc. per liter of methyl ethyl ketone preconditioned by from2 to 5% concentrated sulphuric acid and neutralized with an excess ofalkali.

5. An alkali cyanide zinc plating bath comprising as an addition agentmaterial obtainable by treating one or more ketones with a condensationcatalyst selected from the group consisting of sulphuric acid andhydrochloric acid.

6. An alkali cyanide zinc plating bath comprising as an addition agentfrom 5 to cc. per liter of material obtainable by treating methyl ethylketone with a condensation catalyst selected from the group consistingof sulphuric acid and hydrochloric acid.

VINCENT MA'I'IACO'I'I'I.

